Thermal spray coatings can be used for the protection of equipment and components used in corrosive environments. Such thermally sprayed coatings are derived from the heating, acceleration of materials, originally in solid form as powder or wire, through a thermal spray device in which they are rendered semi-molten and deformable prior to impact on a work piece surface. As such, they contain differing degrees of residual porosity which may range in size from the clearly visible to the sub-micron. Much of the porosity is interconnected and forms networks of surface-to-substrate channels into which corrosive process gases may penetrate. Corrosion of the coating, or of the substrate if penetration is complete, is unacceptable in coated equipment used in integrated circuit manufacture because of the generation of contaminant corrosion products and particles.
U.S. Pat. No. 5,869,144 discloses a process for sealing the outer porous surface of an article with a boron nitride-silicate-containing sealant. Articles, i.e., rolls, intended for use with molten zinc are coated with a protective layer such as tungsten carbide cobalt, alumina, zirconia or molybdenum boride. The sealant is then deposited over the coating to prevent penetration of molten zinc to the substrate of the roll and also to minimize buildup of oxides and/or dross on the surface of the coated roll from the molten zinc.
There is a need in the art for blocking or sealing the inter-connected residual micro-porosity in thermal spray coated and sintered articles, including metallic and carbide-based coatings operating at high temperatures, but particularly those of the ceramic oxides, e.g., yttria and alumina, to reduce the level of corrosive attack by process reagents. There also is a need for blocking or sealing the porosity especially in coatings or sintered bodies used in equipment employed in integrated circuit manufacture without using any hydrocarbon or other resin systems, or without introducing any foreign metal cations, mobile or otherwise, or without causing any coloration or reduction in whiteness of the coating.